WEDNESDAY, June 18, 2014 (HealthDay News) -- A popular class of drugs used to treat inflammatory bowel disease isn't linked to an increase in the short-term risk of cancer, Danish researchers report.

Researchers found that people with Crohn's disease or colitis who received the drugs -- tumor necrosis factor alpha (TNF-a) antagonists -- had about the same risk of cancer as other people with these inflammatory bowel diseases who were not treated with the medication.

The drugs work by interrupting the function of TNF-a, a substance used by the immune system to increase inflammation.

"Treatment with these drugs inhibits the inflammatory response in the gastrointestinal tract thereby leading to reduced symptoms," said lead author Dr. Nynne Nyboe Andersen of the Statens Serum Institute in Copenhagen.

The problem is that TNF-a also serves a key role in protecting the body against cancer, raising concerns that inhibiting its function could increase a person's risk of cancer.

"It's one of the actual bullets that the immune system uses to shoot down and kill cancer cells or a cell that is infected by a bacteria or a virus," said Dr. Fadi Braiteh, an oncologist with Comprehensive Cancer Centers of Nevada, a US Oncology Network affiliate. "By cooling down the immune system, you can improve the ability of cancer cells to escape detection and develop into full-blown cancer."

A 2006 analysis of earlier clinical trials highlighted this fear, reporting that anti-TNF-a drugs caused a more than threefold increase in cancer risk among patients, the Danish researchers reported in background material. However, three subsequent analyses failed to confirm this finding.

To test the safety of anti-TNF-a drugs, Andersen and colleagues studied cancer rates in more than 56,000 Danish patients with inflammatory bowel disease. They compared the occurrence of cancer in people who had taken the medications to those who had not.

The investigators found that cancer occurred in nearly 7 percent of patients who had never taken anti-TNF-a drugs, compared with just under 2 percent of patients who had been treated with the drugs.

"These results did not reveal any significantly increased risk of cancer," Andersen said. They also found no association between the drugs and any site-specific cancers.

However, the authors noted that follow-up for patients treated with the drugs lasted about four years, making it impossible to say whether they would have an increased risk of cancer over the long term.

Braiteh believes that overall cancer risk does not increase when anti-TNF-a drugs are used because cancer risks are exchanged, cancelling each other out.

Crohn's disease and colitis increase a person's risk of colon cancer due to the constant inflammation, he said. By cooling down the inflammation with these drugs, you reduce a person's risk of colon cancer but potentially increase their risk of developing other forms of cancer.

"We may be decreasing your risk of colon cancer, but slightly increasing your risk of other cancers, so the net balance is zero," Braiteh said. "Maybe we're trading a risk of colon cancer for other cancer, but the net balance is even."